Most consumers have come to expect scented laundry products and to expect that fabrics which have been laundered to also have a pleasing fragrance. It is also desired by consumers for laundered fabrics to maintain the pleasing fragrance over time. Perfume additives make laundry compositions more aesthetically pleasing to the consumer, and in some cases the perfume imparts a pleasant fragrance to fabrics treated therewith. However, the amount of perfume carry-over from an aqueous laundry bath onto fabrics is often marginal and does not last long on the fabric. Fragrance materials are often very costly and their inefficient use in rinse added fabric softener compositions and ineffective delivery to fabrics from the rinse results in a very high cost to both consumers and fabric softener manufacturers. Industry, therefore, continues to seek with urgency for more efficient and effective fragrance delivery in fabric softener products, especially for improvement in the provision of long-lasting fragrance to the rinsed fabrics.
Acetals and ketals have long been known in perfumery. See Steffen Arctander, "Perfume and Flavor Chemicals", Arctander, N.J., 1969. The majority of these are methyl and ethyl types, and molecular weights may range widely. See, for example, Arctander abstract numbers 6, 11, 210, 651, 689, 1697, 1702, 2480, 2478. For 2478, which is phenylacetaldehyde dicitronellyl acetal, molecular weight 414.7, Aictander reports ". . . and it is not exaggerated to say that this acetal is practically abandoned and obsolete in today's perfumery". For 2480, which is phenylacetaldehyde digeranyl acetal, Arctander reports "the title material does not offer substantial advantages or unique odor type and it may be considered of little more than academic interest today". This latter material was still commercially available in 1992 as ROSETAL A (Catalogue, IFF).
Carrier mechanisms for perfume delivery, such as by encapsulation, have been taught in the prior art. See for example, U.S. Pat. No. 5,188,753.
U.S. Pat. No. 5,378,468, Suffis et al, issued Jan. 3, 1995 describes specific types of personal care compositions, such as deodorant sticks, comprising assertedly "body-activated" fragrances. The term apparently refers to the previously known tendency Of materials such as acetals derived from fragrance alcohols to hydrolyze under acidic pH conditions thereby releasing fragrance. See, for example, U.S. Pat. No. 3,932,520, Hoffman, issued Jan. 13, 1976.
Factors affecting substantivity of fragrance materials on fabrics are discussed in Estcher et al. JAOCS 71 p. 31-40 (1994).
The selected potential fragrance materials described by Suffis et al include particular acetals and ketals, exemplified by propylene glycol vanillin acetal. The materials exemplified apparently are rather hydrophilic short chain alcohol or diol derivatives of fragrance aldehydes and upon hydrolysis, deliver one mole of the aldehyde per mole of the potential fragrance material. The present inventors believe that short chain hydrophilic acetal materials are incompatible with acidic rinse added fabric softening compositions as described hereinafter. The Suffis et al development is designed to be incorporated with a personal care product vehicle, resulting in clear deodorant sticks and the like.
For rinse added fabric softening use, it is important that rather hydrophobic pro-fragrant compounds be used in order to enhance deposition onto surfaces in the wash solution and retention on the washed surface during rinsing. In Suffis et al, the compositions containing the potential fragrance materials are applied directly to the substrate (i.e. skin); therefore, the deposition problems resulting from dilution, rinsing, etc. are not at issue.
Acetals and ketals are conventionally known to be stable in basic, and unstable in acidic media. Indeed, acetals are frequently used in chemical synthesis as protecting groups for alcohols and aldehydes in basic pH systems. See, for example, March, Advanced Organic Chemistry, 3rd Ed., pp. 329-332 (Wiley, N.Y., 1985). When used as a protecting group, subsequent treatment of an acetal under acidic conditions liberates the parent alcohol and aldehyde.
It has now been discovered that pro-fragrance and pro-accord acetal and ketals compounds are surprisingly stable in the context of rinse added fabric softening compositions. While as not to be limited by theory, it is believed that this surprising enhancement in stability results from an interaction between the acetal pro-perfume and the fabric softening agents described herein. Specifically, it is believed that the hydrophobic pro-perfume associates with the vesicles contained in the product and is thereby protected from the acidic aqueous (continuous) phase of the product.